The present invention relates in general to spinal pedicular and interlaminal fixation systems useful for maintaining the vertebrae in a desired relationship. In particular, the invention concerns improvements to the spinal fixation system disclosed in U.S. Pat. Nos. 4,790,297 and 4,913,134 to Eduardo Luque and assigned to the assignee of the present invention.
Segmental spinal fusion plates with bolts and nuts have their genesis in 1948 through the work of Baker and Hoit. Since then, spinal fusion plates have become more sophisticated, as have the bolts and screws used to fix the plates to vertebrae. These fusion plates have been used to maintain certain vertebrae in rigid position relative to each other, for instance to facilitate fusion of a vertebra.
In the last decade, spinal fixation systems have been developed using generally rigid plates which span several vertebrae and are engaged on each side of the spinous process. One such type of spinal fixation system and rigid plate is illustrated in the patents to Steffee, U.S. Pat. Nos. 4,611,581 and 4,696,290. In this system, the spinal plate is provided with a series of openings for receiving the threaded portions of force transmitting members, such as bone screws. This spinal plate, known in the art as the Steffee plate, includes a number of bridge elements between each of the series of openings in the plate, which tend to increase the rigidity of the plate.
Another type of spinal fixation system is shown in the aforementioned patents to Luque, U.S. Pat. Nos. 4,790,297 and 4,913,134. In this system, a spinal fixation plate, known as the Luque plate, is described which includes a single elongated opening that extends substantially along the length of the plate. A number of scallops or depressions are formed in the top surface of the plate at the edge of the central opening. The scallops are used to engage a convex portion of a force-transmitting member, such as a bone screw. The system also includes plate ring means which prevents the plate from spreading when the bone screws are tightened down onto the scallops of the plate.
While the Luque system has proven very effective in spinal fixation, practitioners in the field of spinal implants have sought improvements to the system to render them more easily used and adapted to a variety of procedures. In addition, improvements to the systems have been sought to reduce the trauma to the vertebrae or surrounding tissue during and after implantation. While the need for improved usability and atraumatic characteristics is important, any improved system cannot sacrifice the essential beneficial performance of prior plate systems, such as the Luque system described in the above patents.